There is NO regular train that takes 5 minutes longer....the Sobu line (JR) takes 30-40 minutes longer to Tokyo than the 1 hr Narita express (mainly because it periodically sits in stations to let the Narita Express pass!). The Keisei Line is a great option if you find a place around Ueno, and it is Y1,000 cheaper. One advantage of Ueno is you could visit the Japanese art museum in Ueno park.

Regular limited expresses on the Keisei line can be good, but for some of them, you have to change trains along the way and how (or whether) to do that isn't made obvious to occasional visitors who are non-Japanese speakers.

I think maybe parra was referring to the Keisei Skyliner? That doesn't take much longer than the NEX, although you do end up in Ueno or Nippori.